Method and network element for voice-over-IP (VoIP) communications in a mobile IP network

ABSTRACT

A method is performed by one or more network elements for voice-over-IP (VoIP) communications. The method includes receiving a request from a first mobile device to invite a second mobile device to participate in a VoIP session. The second device may be identified in the request by a network identifier. The network identifier is related to a mobile IP (MIP) address of the second device and a second IP address. An invitation is sent to the MIP address of the second device which may include a MIP address of the first device and a first IP address. A response to the invitation may be received from the second device. The response may be modified to include a first IP header that includes the MIP address of the second device and a second IP header to include the second IP address. The modified response is forwarded to the first device. After receipt of the modified response, the first device is configured to establish an IP connection for VoIP communication with the second device.

RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.11/027,915, filed Dec. 30, 2004, now issued as U.S. Pat. No. 7,593,390,which is incorporated herein its entirety by reference.

TECHNICAL FIELD

Embodiments of the invention relate to voice-over-IP technologyimplemented on a mobile wireless broadband network.

BACKGROUND

Voice-over-IP (VoIP) technology permits parties to communicate orallyover a packet-switched IP network. VoIP technology has grown inpopularity, and depending upon certain factors, can offer sound qualitythat is comparable to that of the public switched telephone network(PSTN).

Also growing in popularity are wireless mobile networks. Wireless mobilenetworks permit a device to link to a network without requiring aphysical conductive line to carry data between the device and thenetwork. Further, such networks permit mobility by allowing a device tochange access points in a manner transparent to network elements ornodes outside of the wireless mobile network domain.

Despite the growing popularity of VoIP technology and wireless mobilenetworks, there are no mobile client devices for present VoIP servicesover the Internet. One factor that hinders the advancement such mobiledevices relates to finding a simple scheme by which a mobile device maybe permitted to roam a significant geographic area (and thereforepotentially wander between domains), while appearing keep a single IPaddress. The user datagram protocol (UDP) indexes connections by use ofa quadruplet that contains the IP addresses and port number of bothconnection endpoints. Changing any one of these four numbers causes theconnection to be disrupted and lost. Therefore, it is important that thedevice appear to keep the same IP address while roaming geographically.The difficulty in addressing this issue grows as the geographic areathrough which a device is permitted to roam grows.

From the foregoing, it is evident that there exists a need for a schemeby which a wireless IP telephony device can be permitted to roam ageographically significant area, such as a metropolitan area. It isdesirable that such a scheme be relatively simple to implement as anoverlay to an existing wireless network. It is further desirable thatsuch a scheme be easily interconnected to the PSTN.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a network environment in which an embodiment of a voicehome agent is deployed.

FIG. 2 depicts a protocol stack making up a voice home agent, accordingto an embodiment of the invention.

FIG. 3 depicts a tunneling scheme employed by the mobile IP layer of theprotocol stack depicted in FIG. 2.

FIG. 4 depicts a method of initiating a VoIP phone call, according to anembodiment of the invention.

FIG. 5 depicts a method of executing a VoIP phone call, according to anembodiment of the invention.

FIG. 6 depicts a hardware environment in which a voice home agent may beembodied, according to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 depicts a network environment 100 in which one or more mobilenodes 102 may be permitted to roam over a geographically significantarea, such as across a metropolitan area. The mobile nodes 102communicate via digital transmission (typically in the 2-to-6 GHzlicensed bands, with typical channel bandwidths ranging from 1.5 to 20MHz) to an access point 104. An access point (also referred to herein asa base station), such as the one identified by reference numeral 104,receives transmissions from the mobile node, and communicates thetransmissions to network elements within an associated regional accessnetwork 106. According to an embodiment, the regional access network 106is a wired network (i.e., a physical line interconnects the variouselements making up the regional access network) that is a generic packetbased access network, such as an Ethernet network, an IP/MPLS network,or an ATM network. The transmission between the access points 104 andthe mobile nodes 102 is compliant with Institute of Electrical andElectronics Engineers (IEEE) 802.16 standard signals, IEEE std.802.16-2001, published 2001 and later versions (hereinafter IEEE 802.16standard or IEEE 802.16e standard). A regional access network 106interconnecting access points (such as 104) compliant with IEEE 802.16estandards is referred to as a WiMAX network.

At the periphery of the WiMAX regional access network 106 is a radionetwork services node 108. The radio network services node 108 providesrouting and control between other WiMAX regional are networks, such asthe WiMAX network identified by reference numeral 110. Each regionalaccess network 106 and 124 includes a radio network services node thatcouples the regional access network 106 or 110 to a WiMAX core network112, which interconnects all of the regional access networks 106 and110. Although the WiMAX core network 112 is depicted in FIG. 1 asinterconnecting two WiMAX networks 106 and 110, the WiMAX core network112 may, in principle, interconnect any number of regional accessnetworks.

The WiMAX core network 112 may be an ordinary IP network, composed ofcommonplace IP network elements, such as optical networking elementspermitting high speed data transfer. As such, the WiMAX core network 112may interconnect directly with the Internet (not depicted in FIG. 1).

At the periphery of the WiMAX core network 112 are one or more voicehome agents 114 and 116. There exists a voice home agent 114 or 116associated with each WiMAX regional access network 106 and 110. Thestructure of, and methods enacted by, a voice home agent 114 or 116 arediscussed in detail below. Briefly, a voice home agent is a networkelement that permits VoIP integration between a WiMAX core network (suchas core network 112) and the public switched telephone network (PSTN).Additionally, a voice home agent provides functionality that permits amobile node (such as mobile node 102) to roam from one WiMAX regionalaccess network (such as network 106) to another (such as 110).

Although FIG. 1 depicts a single voice home agent 114 or 116 associatedwith each regional access network 106 or 110, more than one voice homeagent may be associated with a given regional access network. Thus,although reference numerals 114 and 116 are presented herein asreferring to a single voice home agent, each reference numeral 114 and116 may be understood as referring to a group of voice home agentsservicing their respective WiMAX regional access networks 106 and 110.

Each voice home agent 114 and 116 interfaces the WiMAX core network 112to a local office 118 or 120 of the public switched telephone network122. The public switched telephone network 122 uses an out-of-bandsignaling scheme known as Signaling System 7 (SS7), defined by theInternational Telecommunication Union (ITU) TelecommunicationStandardization Sector (ITU-T). An out-of-band signaling scheme employsa different physical path for call control than is used to carry thecontent of the call itself (e.g., the voice data). Therefore, as shownin FIG. 1, a voice home agent serves as two separate interfaces: aninterface for voice data, which is delivered as time domain multiplexeddigital voice data, and an interface for SS7 control signals, which aredelivered as SS7 packets.

A mobile node, such as the one identified by reference numeral 102, maybe embodied as a telephone handset (in like fashion as a cellulartelephone), may be embodied as a personal digital assistant, or may beembodied as another mobile computing device. Upon power-up, a mobilenode makes an initial transmission to the nearest available accesspoint. At the time of transmission, the access point assigns the mobilenode a management channel, which identifies the mobile node to theaccess point. The access point and mobile node may communicate withanother over a distance ranging from one to five or ten miles. Given thesize of such an area, other mobile nodes may be located therein.Therefore, an access point may communicate with hundreds of mobilenodes. The use of management channels permits an access node todistinguish one access point from another.

Each access point in a WiMAX regional access network has an IP addressthat identifies it. However, this IP address is functional only withinthe regional access network (also referred to as a domain) in which theaccess point is situated. Thus, an access point may directly send datato another access point within the regional access network in which itis situated. To direct data to an access point in another domain, theradio network services node servicing the particular domain in which theaccess point is situated must be used as an intermediary.

As mentioned above, during power-up of the mobile node, an initialtransmission is made to the base station for the sake of establishing amanagement channel and authenticating the user. Thereafter, the mobilenode makes an initial communication with the voice home agent servicingthe domain in which the mobile node is situated. This communicationmarks the beginning of a registration process, by which the mobile nodeinforms the voice home agent of which domain the mobile node is in. Inresponse, the voice home agent assigns the mobile node an IP address,known as a mobile IP (MIP) address. The voice home agent also records acare-of address for the mobile node. The MIP address for the mobile nodedoes not change, even should the mobile node wander to a geographicregion in which it communicates with another access point or withanother WiMAX regional access network altogether. The care-of address,on the other hand, identifies the domain with which the mobile node iscommunicating, and therefore changes when the mobile node roams from oneregional access network to another.

A voice home agent may assign a mobile node more than one IP addresses.For example, a mobile node may have one IP address assigned to it forthe carrying of voice data, and another IP address assigned to it forthe carrying of signaling data. For the sake of simplicity, thedisclosure proceeds from the assumption that each mobile node has asingle IP address assigned to it during registration.

At the time of registration, the voice home agent updates a databasethat it maintains. The database may contain information concerning thefeatures supported by the mobile node (call waiting, voicemail, etc.).The database is updated to associate a telephone number by which themobile node is identified, the MIP address assigned to the mobile node,and the domain in which the mobile node is located (i.e., the care-ofaddress of the mobile node).

A WiMAX regional access network 106 or 110 employs a technique known astunneling. By virtue of this technique, movement of a mobile node withina geographic area served by a given WiMAX domain 106 or 110 istransparent to network elements or nodes outside of the domain. Thus,for example, a network node outside of WiMAX domain 106 cannot tellwhether mobile node 102 is communicating with access point 104 or accesspoint 122. A network element outside of the domain 106 need only knowthat the mobile node 102 is located in domain 106 to communicate withthe mobile node 102. Therefore, whenever a mobile node (such as mobilenode 102) moves from one domain to another, the mobile node re-registerswith the voice home agent it previously registered with. In response,the voice home agent updates its database to associate a new care-ofaddress (i.e., network address of the domain with which the mobile nodecommunicates) with the mobile node.

The preceding discussion focused on a network environment in which avoice home agent 114 or 116 operates. The following discussion brieflypresents protocol layers making up a voice home agent 114 or 116.

FIG. 2 depicts a protocol stack 200 executed by the voice home agent 114or 116. As can be seen from FIG. 2, the protocol stack 200 includes aMobile IP (MIP) layer 200 that provides functionality complying with anindustry-accepted MIP standard, such as the standard described in “IPMobility Support,” C. Perkins, ed., IETF RFC 2002, October 1996. Thefunctionality provide by the MIP layer 202 is made available to theupper layers 204-210 of the stack 200.

The MIP layer provides the tunneling functionality mentioned above. FIG.3 depicts the MIP layer 202 receiving a packet 300 having an IP header302. The IP header 302 contains the MIP address assigned to a particularmobile node in its 32-bit destination IP address field, and it thereforetermed IP Header_(MIP). In response to receiving such a packet 300, theMIP layer 202 appends the packet 300 to a second IP header 304. Thesecond IP header uses the care-of address of the particular mobile nodeidentified by the MIP address, and is therefore termed IPHeader_(CareOf). Thus, the WiMAX core network 112 observes the second IPheader 304 and routes the packet 300 according to the second IP header304, meaning that the packet 300 is routed to the appropriate domain 106or 124. Prior to reception by the mobile node, the second IP header 304is stripped away.

The effect of the tunneling technique described with reference to FIG. 3is that each mobile node receives IP packets containing the MIP addressassigned to it during the registration process. Accordingly, each mobilenode may roam-even roam between domains—while retaining the IP addressassigned to it during the registration process.

Many layers of tunneling may be used in the network environment 100depicted in FIG. 1. For example, each WiMAX regional access network 106and 124 may employ tunneling, so that elements laying outside the domainneed only address IP packets to the proper domain in order for thepacket to reach the desired mobile node.

Returning to FIG. 2, it can be seen that the protocol stack 200 alsoincludes a VoIP layer 204, which provides voice over IP functionalitythat may be compliant with an industry-accepted VoIP standard, such asRealtime Transport Protocol (RTP), which is defined by IETF RFC 1889and/or Realtime Streaming Protocol (RTSP), which is defined by IETF RFC2326. Briefly, the VoIP layer 204 receives VoIP packets and transformsthose packets into time domain multiplexed digital voice data for thepublic switched telephone network (PSTN) 118 and 120, and vice versa. Asdiscussed below, in the context of a discussion between a user of amobile node and a user of the PSTN, the VoIP layer 204 converts timedomain multiplexed digital data into VoIP packets. The VoIP packetscontain the MIP address assigned to the particular mobile node. The VoIPpackets are passed to the MIP layer 202, which appends the VoIP packetsto an IP header containing the care-of address of the particular mobilenode.

The protocol stack 200 also includes a session initiation protocol layer206, which provides SIP functionality that may be compliant with anindustry-accepted standard, such as IETF RFC 3261. Briefly, the SIPlayer 206 provides application-layer control functionality for creating,modifying, and terminating communication sessions with one or moreparticipants. For example, the SIP layer 206 contains the functionalityto signal a mobile node that another party wishes to communicate withit.

The protocol stack 200 also includes a layer 210 that interfaces withthe PSTN. The layer 210 includes a media gateway (MGW) that convertstime-domain multiplexed voice data into IP packets. It also includes anSS7 interface that receives SS7 signals, decodes the signals, and passesthe extracted information to the voice home agent control plane 208.

The voice home agent control plane 208 coordinates the actions of theother layers. It mediates communication between the major gateway andthe VoIP layer 204, and also mediate communication between the SS7interface and the SIP layer 206. For example, the voice home agentcontrol plane 208 may receive a signal from the SS7 interface 210indicating that a connection to a particular telephone number isdesired. In response, the control plane 208 invokes the SIP plane 206 tosend an SIP invite message to the mobile node corresponding to thetelephone number. Similarly, the control plane 208 receives voice datain a particular time slot and forwards the data to the VoIP layer forconversion into VoIP packets, and for communication to particular mobilenode (in this way, a voice path is maintained).

The preceding discussion briefly presented protocol layers 202-210making up a voice home agent 114 or 116. A discussion relating to theoperation of the voice home agent 114 or 116 with respect to callinitiation and call execution follows. This discussion describes theoperation of the voice home agent as a whole (as opposed to on alayer-by-layer basis), and provides an high-level integrated view of theoperation of the voice home agent.

FIG. 4 depicts the operation of a voice home 114 or 116 agent ininitiating a telephone call to a mobile node. The process may beinitiated by a user of the PSTN or by a user of a mobile node served bythe voice home agent 114 or 116. If the process is initiated by a userof the PSTN, then the voice home agent 114 or 116 receives an SS7 signalindicating that a telephone call is desired with a mobile nodeidentified by a particular telephone number, as shown in operation 400.The telephone number is extracted from the SS7 signal (operation 400).The SS7 signal is converted into an invite message (operation 400),which is an SIP message indicating that a communication session isdesired. Thus, at the completion of operation 400, the voice home agent114 or 116 has constructed an invite message addressed to a particulartelephone number.

On the other hand, the process may have been initiated by a mobile nodeserved by the voice home agent 114 or 116. When a mobile node initiatesthe phone call, the mobile node sends an SIP invite message addressed toa chosen telephone number to the voice home agent 114 or 116. This SIPinvite message is received by the voice home agent, as shown inoperation 402.

Whether the SIP invite message is received (as is the case when a mobilenode initiates the phone call) or is created by the voice home agent (asis the case when a user of the PSTN initiates the phone call), operationflow next proceeds to operation 404. In operation 404, the voice homeagent queries a database to identify a MIP address and care-of addressassociated with the telephone number embedded in the invite message.

If the telephone number identified in operation 404 corresponds to thedomain served by the voice home agent 114 or 116, then the voice homeagent 114 or 116 sends the SIP invite message to the mobile node usingthe tunneling technique described with reference to FIG. 3 (operation406).

If the telephone number identified in operation 404 corresponds to adomain not served by the voice home agent 114 or 116, then the voicehome agent 114 or 116 sends the SIP invite message to the voice homeagent 114 or 116 serving the domain corresponding to the invited mobile(operation 408).

If the telephone number indicates that the telephone number refers to atelephony device served by the PSTN, the invite message is converted toan SS7 signal to originate the phone call on the PSTN (operation 410).

After the invite message has been sent (by way of an SIP invite messageor by way of an SS7 signal), the voice home agent 114 or 116 awaits aresponse to the invite message, as shown in operation 412. If the userof the invited telephony device wishes to answer the phone call, aresponse indicating such a desire is received by the voice home agent114 or 116 (operation 412). If the response originates from a mobilenode, the response may reach the voice home agent 114 or 116 in the formof an SIP acknowledge (ack) message. On the other hand, if the responseoriginates from a PSTN telephony device, the response may come to thevoice home agent 114 or 116 in the form of an SS7 signal that may beconverted into an SIP ack message.

After the response is received, it is forwarded to the initiator(operation 414). If the initiator of the phone call is a mobile node,the forwarding operation involves sending the response to the mobilenode, using MIP layer 202 to employ the tunneling technique describedwith reference to FIG. 3. On the other hand, if the initiator of thephone call is a telephony device on the PSTN, then the response isconverted into an SS7 signal, and is directed to the PSTN through theSS7 interface 210.

Finally, assuming the response received in operation 412 indicates thatthe user of the invited mobile node wishes to engage in a communicationsession (i.e., wishes to answer the call), a voice path between theinviting and invited devices is established (operation 416).Establishing the voice path may involve associating a particular timeslot in the time-domain multiplexed voice data from the PSTN localoffice 118 or 120 with a particular MIP address (and vice versa).Additionally, it may involve associating an MIP address of a mobile nodewith a care-of address or an address of a voice home agent 114 or 116servicing a particular mobile node.

After a VoIP session has been established (as shown in FIG. 4), theparties may speak to one another. While the parties speak, the voicehome agent 114 or 116 receives either VoIP packets or time-domainmultiplexed voice data from the PSTN, as shown in operation 500 of FIG.5. If the voice home agent receives time-domain multiplexed voice datafrom the PSTN, such data is converted to VoIP packets, as discussedabove.

Next, as shown in operation 502, the VoIP packets or voice data are sentalong the voice pathway established in operation 416 of FIG. 4. In thecase of sending VoIP packets to a mobile node, this may mean sendingreceived VoIP packets to a voice home agent 114 or 116 servicing themobile node, or may mean directly sending received VoIP packets to amobile node, using the tunneling technique described with reference toFIG. 3. In the case of sending voice data to telephony device on thePSTN, operation 502 includes converting VoIP data to time-domainmultiplexed digital voice data, and inserting such voice data into anappropriate time slot, so that the PSTN switching equipment routes thedata to the appropriate location.

The preceding discussion related to the operation of the voice homeagent during initiation and execution of a phone call. The followingdiscussion presents, from a system-level point of view, initiation andexecution of a phone call in the context of the network environment 100depicted in FIG. 1.

In the context of a telephone call between a PSTN telephony device(initiator of call) and a mobile node (responder to call), the flowproceeds as follows. Initially, the voice home agent 114 or 116 receivesan SS7 signal indicating that a communication session is desired with amobile device corresponding to a given telephone number. The voice homeagent extracts the telephone number, and creates an SIP invite messageaddressed to an MIP address of the invited mobile node. (If the invitedmobile node is not available, the call may be re-routed to a voice mailservice.)

By virtue of the tunneling capability of the voice home agent and thevarious WiMAX domains, the SIP invite message reaches the invited mobilenode, addressed to the mobile node's MIP address. Within the SIP invitemessage, caller-ID information is embedded. Therefore, a messageidentifying the inviting telephony device may be displayed at theinvited mobile node. Meanwhile, the voice home agent 114 or 116 sends anSS7 signal resulting in a ring-back tone to the inviting telephonydevice.

If the user of the mobile node accepts the call, then an SIPacknowledgement message is sent to the voice home agent 114 or 116. Thevoice home agent 114 or 116 translates the SIP acknowledgement messageinto an SS7 signal, and establishes a voice path. At this time, theusers of the PSTN telephony device and the mobile node begin speaking.

In the context of a telephone call between two mobile nodes (indifferent domains), the flow proceeds as follows. Initially, the voicehome agent receives an SIP invite message from the inviting mobile node.The SIP invite message is addressed to a telephone number correspondingwith the desired mobile node. In response, the voice home agent forwardsthe SIP invite message to the voice home agent servicing the domain inwhich the invited mobile node is located. The latter voice home agentsends the response to the MIP address of the invited mobile node.

By virtue of the tunneling capability of the voice home agent and thevarious WiMAX domains, the SIP invite message reaches the invited mobilenode, addressed to the mobile node's MIP address. Within the SIP invitemessage, caller-ID information is embedded. Therefore, a messageidentifying the inviting telephony device may be displayed at theinvited mobile node. Further, the IP address of the inviting mobile nodeis contained in the SIP invite message.

If the user of the invited mobile node accepts the call, then an SIPacknowledgement message is sent to the voice home agent 114 or 116servicing the domain in which the invited mobile node is located. Inresponse, the voice home agent 114 or 116 forwards the SIPacknowledgement message to the voice home agent 114 or 116 servicing thedomain in which the inviting mobile node is located. The latter voicehome agent 114 or 116 forwards the SIP acknowledgement message to theinviting mobile node's MIP address. The SIP acknowledgement messagecontains the IP address of the invited node.

Voice communication may now occur in one of two manners. First, themobile nodes may communicate with one another without the mediation ofvoice home agents. This is possible because, by virtue of the SIP inviteand acknowledgement message, each mobile node is aware of the other's IPaddress. However, the connection between the two mobile nodes will belost, should either of the mobile nodes roam to a different domain.

Secondly, the voice path may extend between both voice home agents. Thisscheme allows for either of the mobile nodes to roam from domain todomain.

FIG. 6 depicts a hardware environment in which the voice home agent 114or 116 may be embodied. The environment includes four blades 600, 602,604, and 606. Each blade contains its own computing environment,including a processor, a memory, and an input/output module (control huband I/O bus, for example) providing access to a network interface or tostorage. Each blade 600-606 may communicate via a local area network,such as via an Ethernet hub. The blades 600-606 may be embodied as thinboards that may be mounted within a rack.

Each blade may be dedicated to executing various facets of thepreviously described control plane functions or data plane functions.For example, blade 602 may execute the functions relating to the MIPlayer 202. This blade 602 also executes the routing functionalityrequired when a VoIP packet is received, and needs to be routed toanother voice home agent, or to a mobile node, as described above. Theblade 602 includes a network interface to permit the software/firmwareexecuted thereon to communicate with the WiMAX core network 112.

Blade 604 may execute the VoIP functionality described above withreference to the VoIP layer 204 discussed in FIG. 2. The blade 604includes a time domain multiplexing interface to permit thesoftware/firmware executed thereon to interact with time domainmultiplexed digital voice data from the PSTN.

Blade 606 may decode SS7 signals and send the extracted content to theSS7 application layer functionality residing on blade 600. The blade 606includes an SS7 interface to permit the software/firmware executedthereon to interact with the SS7 packets from the PSTN local office.

Blade 600 may execute the voice home agent control plane functionalitydescribed above. For this purpose, the blade includes a storage device(to maintain the database necessary to enact such functionality). Theblade 600 also executes the SIP functionality and application layerfunctionality of the SS7 subsystem. In one embodiment, the blade 600executes a billing routine. The billing routine may track, on auser-by-user or account-by-account basis, the amount of time a givenuser is connected to the network, the amount of traffic consumed by theuser, the type of service consumed (local call, long distance call,etc.) by the user, or the bandwidth consumed by the user. The trackedinformation may be stored in a database, and periodic bills may begenerated therefrom.

Embodiments of the invention may be implemented in one or a combinationof hardware, firmware, and software. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by at least one processor to perform theoperations described herein. A machine-readable medium may include anymechanism for storing or transmitting information in a form readable bya machine (e.g., a computer). For example, a machine-readable medium mayinclude read-only memory (ROM), random-access memory (RAM), magneticdisc storage media, optical storage media, flash-memory devices,electrical, optical, acoustical or other form of propagated signals(e.g., carrier waves, infrared signals, digital signals, etc.), andothers.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims.

In the foregoing detailed description, various features are occasionallygrouped together in a single embodiment for the purpose of streamliningthe disclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the subjectmatter require more features than are expressly recited in each claim.Rather, as the following claims reflect, inventive subject matter liesin less than all features of a single disclosed embodiment. Thus, thefollowing claims are hereby incorporated into the detailed description,with each claim standing on its own as a separate preferred embodiment.

1. A method performed by one or more network elements for establishing avoice-over-IP (VoIP) communications session between a firstcommunication device and a second communication device, the methodcomprising: receiving a request from the first communication device toinvite the second communication device to participate in a VoIP session,the second communication device being identified in the request by anetwork identifier; relating the network identifier to a mobile IP (MIP)address of the second communication device and a second IP address, thesecond IP address indicating either a point-of-attachment of the secondcommunication device to a wireless access network or a care-of-addressof a domain of the wireless access network in which the secondcommunication device is located; sending an invitation to the MIPaddress of the second communication device, the invitation including aMIP address of the first communication device and a first IP address;receiving a response to the invitation from the second communicationdevice; modifying the response to include a first IP header thatincludes the MIP address of the second communication device and a secondIP header to include the second IP address; and forwarding the modifiedresponse to the first communication device, wherein after receipt of themodified response, the first communication device is configured toestablish an IP connection for a VoIP session with the secondcommunication device using the MIP address of the second communicationdevice and the second IP address.
 2. The method of claim 1 wherein thefirst IP address indicates a point-of-attachment of the firstcommunication device to the wireless access network.
 3. The method ofclaim 1 wherein the first IP address indicates a care-of-address of adomain of the wireless access network in which the first communicationdevice is located.
 4. The method of claim 3 wherein the invitation thatis sent to the MIP address of the second communication device includesthe care of address of the first communication device when the secondcommunication device is located in a different domain.
 5. The method ofclaim 1 wherein the invitation is a SIP invite message that isconfigured in accordance with a session initiation protocol (SIP), andwherein the response to the invitation is a SIP acknowledge message. 6.The method of claim 5 wherein the SIP invite message includes caller IDinformation identifying the first communication device.
 7. The method ofclaim 1 wherein the invitation is an invitation to participate in theVoIP session, and wherein the response indicates that the secondcommunication device accepts the invitation to participate in the VoIPsession.
 8. The method of claim 1 wherein after receipt of the modifiedresponse, the first communication device is configured to establish apeer-to-peer IP connection for VoIP communication with the secondcommunication device, the peer-to-peer IP connection including acommunication path that does not include the one or more networkelements.
 9. The method of claim 1 wherein after receipt of the modifiedresponse, the first communication device is configured to establish theIP connection using a tunneling technique for VoIP communication withthe second communication device.
 10. The method of claim 1 wherein thefirst communication device is located in a first domain serviced by afirst network element, and wherein when the network identifier relatesto a second domain of the wireless access network, the method includesforwarding the invitation to a second network element that is servicingthe second domain, the second communication device being located in thesecond domain.
 11. The method of claim 1 wherein after receipt of themodified response, the first communication device is configured toestablish an IP connection for VoIP communication with the secondcommunication device, the IP connection including a communication paththat includes one or more network elements to allow at least one of thefirst and second communication devices to roam between domains.
 12. Themethod of claim 1 further comprising: determining if the firstcommunication device has changed a point of attachment to the network;and redefining the first IP address to identify the changed point ofattachment.
 13. The method of claim 1 wherein the VoIP communicationscomprise audio and video phone calls communicated through apacket-switched IP network.
 14. The method of claim 1 wherein the firstand second communication devices are configured to communicate packetsover the established IP connection, the packets including at least oneof voice and video data.
 15. The method of claim 14 wherein the firstand second communication devices comprise mobile devices.
 16. The methodof claim 14 wherein the first and second communication devices comprisemobile communication nodes configured to operate in a broadband wirelessaccess network, wherein the first and second communication devicescomprise cellular telephones, and wherein the one or more of the networkelements comprise a radio network-servicing node.
 17. The method ofclaim 14 wherein the one or more network elements comprise a voice homeagent.
 18. A network element configured to establish a voice-over-IP(VoIP) communications session between a first communication device and asecond communication device, the network element configured to: receivea request from the first communication device to invite the secondcommunication device to participate in a VoIP session, the secondcommunication device being identified in the request by a networkidentifier; relate the network identifier to a mobile IP (MIP) addressof the second communication device and a second IP address, the secondIP address indicating either a point-of-attachment of the secondcommunication device to a wireless access network or a care-of-addressof a domain of the wireless access network in which the secondcommunication device is located; send an invitation to the MIP addressof the second communication device, the invitation including a MIPaddress of the first communication device and a first IP address;receive a response to the invitation from the second communicationdevice; modify the response to include a first IP header that includesthe MIP address of the second communication device and a second IPheader to include the second IP address; and forward the modifiedresponse to the first communication device, wherein after receipt of themodified response, the first communication device is configured toestablish an IP connection for a VoIP session with the secondcommunication device using the MIP address of the second communicationdevice and the second IP address.
 19. The network element of claim 18wherein the first IP address indicates a point-of-attachment of thefirst communication device to the wireless access network.
 20. Thenetwork element of claim 18 wherein the first IP address indicates acare-of-address of a domain of the wireless access network in which thefirst communication device is located.
 21. The network element of claim20 wherein the invitation that is sent to the MIP address of the secondcommunication device includes the care of address of the firstcommunication device when the second communication device is located ina different domain.
 22. The network element of claim 18 wherein theinvitation is a SIP invite message that is configured in accordance witha session initiation protocol (SIP), and wherein the response to theinvitation is a SIP acknowledge message.
 23. The network element ofclaim 22 wherein the SIP invite message includes caller ID informationidentifying the first communication device.
 24. The network element ofclaim 18 wherein the invitation is an invitation to participate in theVoIP session, and wherein the response indicates that the secondcommunication device accepts the invitation to participate in the VoIPsession.
 25. The network element of claim 18 wherein after receipt ofthe modified response, the first communication device is configured toestablish a peer-to-peer IP connection for VoIP communication with thesecond communication device, the peer-to-peer IP connection including acommunication path that does not include the network element.
 26. Thenetwork element of claim 18 wherein after receipt of the modifiedresponse, the first communication device is configured to establish theIP connection using a tunneling technique for VoIP communication withthe second communication device.
 27. The network element of claim 18wherein the network element is a first network element, wherein thefirst communication device is located in a first domain serviced by thefirst network element, and wherein when the network identifier relatesto a second domain of the wireless access network, the first networkelement is configured to forward the invitation to a second networkelement that is servicing the second domain, the second communicationdevice being located in the second domain.
 28. The network element ofclaim 18 wherein after receipt of the modified response, the firstcommunication device is configured to establish an IP connection forVoIP communication with the second communication device, the IPconnection including a communication path that includes one or morenetwork elements to allow at least one of the first and secondcommunication devices to roam between domains.
 29. The network elementof claim 18 further comprising: determining if the first communicationdevice has changed a point of attachment to the network; and redefiningthe first IP address to identify the changed point of attachment.
 30. Amethod for voice-over-IP (VoIP) communications comprising: receiving arequest at a network element from a first communication device to invitea second communication device to participate in a VoIP session, thesecond communication device being identified in the request by a networkidentifier; relating the network identifier to a mobile IP (MIP) addressof the second communication device and a second IP address; sending aninvitation to the MIP address of the second communication device, theinvitation including a MIP address of the first communication device anda first IP address; receiving a response to the invitation from thesecond communication device; modifying the response to include a firstIP header that includes the MIP address of the second communicationdevice and a second IP header to include the second IP address; andforwarding the modified response to the first communication device,wherein after receipt of the modified response, the first communicationdevice is configured to establish an IP connection for a VoIP sessionwith the second communication device using the MIP address of the secondcommunication device and the second IP address, wherein the first IPaddress indicates a point-of-attachment of the first communicationdevice to a wireless access network; and wherein the second IP addressindicates a point-of-attachment of the second communication device tothe wireless access network.
 31. The method of claim 30 wherein afterreceipt of the modified response, the first communication device isconfigured to establish a peer-to-peer IP connection for VoIPcommunication with the second communication device, the peer-to-peer IPconnection including a communication path that does not include thenetwork element.
 32. The method of claim 31 wherein the network elementis a first network element, wherein the first communication device islocated in a first domain serviced by a first network element, andwherein when the network identifier relates to a second domain of thewireless access network, the method includes forwarding the invitationto a second network element that is servicing the second domain, thesecond communication device being located in the second domain.
 33. Themethod of claim 32 further comprising: determining if the firstcommunication device has changed its point of attachment to the network;and redefining the first IP address to identify the changed point ofattachment to allow roaming between domains.